Attachment of structures having different physical characteristics

ABSTRACT

Methods of bonding first structures to second structures are disclosed wherein the first and second structures are fabricated materials having different physical characteristics. For example, the first structure may be a composite fan blade and the second structure may be a composite or metallic rotor, both for use in gas turbine engines. The method includes providing the first and second structures and plating or otherwise coating a portion of the first structure with a metal to provide a metal-coated portion. The method includes applying at least one intermediate material onto the metal-coated portion of the first structure. The method further includes bonding the metal-coated portion of the first structure and the intermediate material to the second structure. The bonding is carried out using a relatively low-temperature process, such as liquid phase bonding, including TLP and PTLP bonding. Brazing is also a suitable technique, depending on the materials chosen for the first and second structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a non-provisional patent application claimingpriority under 35 USC § 119(e) to U.S. Provisional Patent ApplicationSer. No. 61/930,510 filed on Jan. 23, 2014.

BACKGROUND Technical Field

This disclosure relates to the bonding, attachment or coupling ofstructures having different physical characteristics, such as thebonding of a composite structure to a metallic structure. Morespecifically, this disclosure relates to turbomachinery, moreparticularly, to various means for bonding composite fan blades or vanesto metallic or composite rotors or hubs.

Description of the Related Art

Turbomachinery fan blades may be secured to a supporting rotor byproviding shaped slots in the rotor that mateably receivecorrespondingly shaped roots of the fan blades. For example, the rotorsmay include dovetail or fir tree shaped slots that receive complementaryshaped roots disposed at the radially inwardly ends of the fan blades.The slots of the rotor and the roots of the fan blades are adapted tolock the fan blades against radial movement as the rotor spins about itsaxis.

Designers of gas turbine engines are constantly seeking ways to reducethe weight of various components. One strategy involves the substitutionof traditional titanium and aluminum alloys as primary constructionmaterials in favor of various composite materials. Composites areattractive because they are typically lighter than titanium or aluminumalloys and exhibit high specific strength and stiffness. Polymer matrixcomposites may be used for many gas turbine engine parts despite theirinability to withstand high temperatures. For example, carbon fiberreinforced polymer composites have been successfully used in thefabrication of fan blades. Metal matrix composites and ceramic matrixcomposites exhibit lower specific strengths, but show promise as theyare able to withstand higher temperatures.

While the design and development of composite fan blades for gas turbineengines is under way, the rotors to which fan blades are attached arestill primarily fabricated from metal alloys. However, the use ofcomposite materials for rotors of fan assemblies is on the horizon.Regardless, because of different structural requirements, fan blades androtors will most likely continue to be fabricated from differentmaterials having different properties. In the case of a composite fanblade and a rotor, a problem arises because of the different materialproperties of the composite used to fabricate the fan blade and themetal alloy or composite material used to fabricate the rotor. Whenmaterials of different characteristics are coupled together, it may bedifficult to provide robust attachment method because, amongst otherreasons, differences in the coefficients of thermal expansion (CTEs) cancompromise the connection between the fan blades and the rotor.

Thus, there is a need for improved techniques for bonding, coupling orattaching a composite structure, such as a composite fan blade, to astructure made from a different material, such as a metallic rotor or acomposite rotor. While this disclosure utilizes fan blades and rotors asa primary example, this disclosure is directed more broadly to methodsof bonding, coupling, or connecting one structure to another structure,wherein the structures are made from different materials havingdifferent material properties.

SUMMARY OF THE DISCLOSURE

In one aspect, a method of bonding a first structure to a secondstructure is disclosed. The first structure may be non-metallic. Themethod may include providing the first and second structures and coatinga portion of the first structure with a metal to provide a metal-coatedportion. The method may further include applying at least oneintermediate material on the metal-coated portion of the firststructure. Further, the method may include attaching the first structureto the second structure by bonding the intermediate material to thefirst and second structures.

In another aspect, a rotor assembly for a gas turbine engine isdisclosed. The disclosed rotor assembly may include a composite fanblade. The fan blade may include a root. The metal rotor may include aslot for receiving the root. The root may be at least partially coatedwith a metal to form a metal-coated portion. The metal-coated portion ofthe root may be at least partially covered with an intermediatematerial. The root, the metal-coated portion and the intermediatematerial may be received in the slot and the intermediate materialbonded to the root and the rotor to thereby attach the fan blade to therotor.

In yet another aspect, a method of bonding a first structure to a secondstructure is disclosed. The method may include providing the firststructure having a first CTE and providing the second structure having asecond CTE, wherein the first and second CTEs are different. The methodmay further include selecting an intermediate material having a thirdCTE that falls between the first and second CTEs. The method may furtherinclude coating a portion of the first structure to provide ametal-coated portion and applying the intermediate material to themetal-coated portion of the first structure. Further, the method mayinclude bonding the first structure to the intermediate material and theintermediate material to the second structure by liquid phase bonding.

In any one or more of the embodiments described above, the coating ofthe portion of the first structure may be performed by plating, metalspraying, impacting the portion of the first structure with a metallicmaterial, applying a metal sleeve to the portion of the first structure,etc.

In any one or more of the embodiments described above, the bondingprocess may be selected from the group consisting of transient liquidphase (TLP) bonding, partial transient liquid phase (PTLP) bonding andbrazing.

In any one or more of the embodiments described above, the secondstructure may be metallic.

In any one or more of the embodiments described above, the first andsecond structures are metallic and the bonding may include diffusingintermediate material into the first and second structures.

In any one or more of the embodiments described above, one of thestructures may be composite and the other structure may be metallic, andthe bonding may include reacting intermediate material with the metalcoating on the composite structure and diffusing intermediate materialinto the metallic structure.

In any one or more of the embodiments described above, both structuresmay be made from composite materials and both structures may bepartially coated with a metal. Further, the bonding may include reactingthe intermediate material with the metal coatings on the compositematerials of both structures.

In any one or more of the embodiments described above, the compositematerial may be selected from the group consisting of polyetherimide(PET), polyimide, polyether ether ketone (PEEK), polyether ketone ketone(PEKK), polysulfone, nylon, polyphenylsulfide, polyester, condensationpolyimides, addition polyimides, epoxy cured with aliphatic and/oraromatic amines and/or anhydrides, cyanate esters, phenolics,polyesters, polybenzoxazine, polyurethanes, polyacrylates,polymethacrylates, and silicones (thermoset). In a further refinement ofthis concept, the composite material may further include fiberreinforcements. In a further refinement, fiber reinforcements may beselected from the group consisting of carbon, glass, or metal fibers.

In any one or more of the embodiments described above, the first andsecond structures may have different coefficients of thermal expansion(CTEs) and the intermediate material may have a CTE that falls betweenthe CTEs of the first and second structures.

In any one or more of the embodiments described above, the intermediatematerial may include a metal foil. However, the intermediate material ormaterials may also be provided in powder form, as a braze paste or theintermediate material may be applied by physical vapor deposition (PVD),electroplating and other techniques that will be apparent to thoseskilled in the art.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods andapparatuses, reference should be made to the embodiments illustrated ingreater detail in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a gas turbine engine;

FIG. 2 is a perspective view of a rotor and fan blade that forms part ofthe fan assembly of the gas turbine engine illustrated in FIG. 1.

FIG. 3 is an end view of a fan blade root.

FIG. 4 is an end view of the fan blade root shown in FIG. 3 after beingcoated with metal.

FIG. 5 is an end view of the fan blade root shown in FIGS. 3 and 4 afteran intermediate material has been applied to the metal-coated portion ofthe fan blade root.

FIG. 6 is a partial end of the fan blade root shown in FIG. 5 installedin a slot of a rotor and bonded to the rotor using one of the techniquesdisclosed herein.

FIG. 7 is a partial perspective view of a fan blade installed on arotor.

FIG. 8 is a flow chart depicting a sample sequence of steps which may bepracticed in accordance with the present disclosure.

It should be understood that the drawings are not necessarily to scaleand that the disclosed embodiments are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosed methodsand apparatuses or which render other details difficult to perceive mayhave been omitted. It should be understood, of course, that thisdisclosure is not limited to the particular embodiments illustratedherein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 is a sectional view of a gas turbine engine 10. The gas turbineengine 10 may include a fan section 11 that, in turn, may include a fanblade assembly 12. The fan blade assembly 12 may be mounted immediatelyaft of a nose 13 and immediately fore of a low-pressure compressor (LPC)14. The LPC 14 may be part of a compressor section 15 and may bedisposed between the fan blade assembly 12 and a high-pressurecompressor (HPC) 16. The LPC 14 and HPC 16 may be disposed fore of acombustor 17, which may be disposed between the HPC 16 and ahigh-pressure turbine (HPT) 18 that is part of a turbine section 19. TheHPT 18 is typically disposed between the combustor 17 and a low-pressureturbine (LPT) 21. The LPT 21 may be disposed fore of a nozzle 22. TheLPC 14 may be coupled to the LPT 21 via a shaft 23, which may extendthrough an annular shaft 24 that may couple the HPC 16 to the HPT 18. Anengine case 25 may be disposed within an outer nacelle 26 that surroundsthe fan section 11.

Turning to FIG. 2, the fan blade assembly 12 may include a plurality offan blades 30 mounted to a rotor 31. More specifically, the rotor 31 mayinclude an outer periphery 32 through which a plurality of dovetailshaped slots 33 extend. The slots 33 may include inner base surfaces 34.The base surfaces 34 may each be disposed between inwardly slantedsidewalls 36, 37 that extend inwardly towards each other as they extendradially outwardly from their respective base surfaces 34. As also shownin FIG. 2, the slots 33 may each accommodate a correspondingly shapedroot 38 of a fan blade 30. The dovetail shaped root 38 may be connectedto a blade or airfoil 39 that includes a leading edge 41 and a trailingedge 42. The leading and trailing edges 41, 42 are disposed on eitherside of the blade tip 43.

Still referring to FIG. 2, the root 38 may include an inner face 44 thatmay be disposed between and connected to inwardly slanted pressure faces45, 46. The pressure faces 45, 46 may each engage the inwardly slantedsidewalls 36, 37 respectively of their respective slot 33 in the rotor31. The pressure faces 45, 46 can wear due to their engagement with theslanted sidewalls 36, 37 of the rotor 31. The application of a metallayer 51 (FIG. 4) and an intermediate layer 52 (FIG. 5) to the pressurefaces 45, 46 may enhance the wear resistance properties of the pressurefaces 45, 46.

While dovetail shaped slots 33 and roots 38 are shown herein, the readerwill note that other types of slots and roots, including but not limitedto fir tree shaped slots and correspondingly shaped roots are alsoclearly applicable to this disclosure and are considered within thespirit and scope of this disclosure.

An exemplary substrate for use in fabricating all or part of the fanblades 30 includes an injection-molded, compression-molded, blow-molded,additively manufactured or a composite-layup piece formed of at leastone of the following: polyetherimide (PEI), polyimide, polyether etherketone (PEEK), polyether ketone ketone (PEKK), polysulfone, nylon,polyphenylsulfide, polyester, condensation polyimides, additionpolyimides, epoxy cured with aliphatic and/or aromatic amines and/oranhydrides, cyanate esters, phenolics, polyesters, polybenzoxazine,polyurethanes, polyacrylates, polymethacrylates, silicones (thermoset),or any of the foregoing with fiber reinforcement of carbon, glass,metal, or other suitable fiber material.

Turning to FIGS. 3-7, FIG. 3 is an end view of a fan blade 30 thatincludes a root 38 with an inner face 44 and pressure faces 45, 46. InFIG. 4, the root 38 has been coated with a metal layer 51. If the fanblade 30 is fabricated from a composite material, plating or coating thecomposite root 38 with a metal enables another metal or metallicmaterial to be bonded to the metal layer 51. Thus, in FIG. 5, the root38 has not only been coated with the metal layer material 51 but a layerof intermediate material 52 has been applied to the metal layer 51. Theintermediate material 52 may be provided in the form of foil, a powderor a braze paste. Foil may be preferred due to the ease of consistentapplication. Further, the intermediate material 52 may be a metallicmaterial applied by PVD, electroplating or another process that will beapparent to those skilled in the art.

In the selection of the intermediate material 52, the CTEs of theintermediate material 52 and the materials of construction of the fanblades 30 and rotors 31 may be considered. For example, if the CTE ofthe composite material used to fabricate the fan blade 30 has a firstvalue and the material used to fabricate the rotor 31 has a CTE of asecond value that is different from the first value, the intermediatematerial 52 may be selected based on its CTE, which may be a third valuethat falls between the first and second values. The intermediatematerial 52 may also be selected for wear resistant properties.

Turning to FIGS. 6 and 7, the fan blade 30 as illustrated in FIG. 5 hasbeen inserted into the slot 33 and the rotor 31 and a bonding processhas been carried out. The bonding process may be transient liquid phase(TLP) bonding, partial transient liquid phase (PTLP) bonding, brazing oranother process that will be apparent to those skilled in the art.Because composite materials are less refractory than other non-metallicmaterials, such as ceramic materials, the bonding process illustrated inFIGS. 6 and 7 may need to be performed at lower temperatures. Thus, TLPand PTLP bonding may be preferred methods because they produced bondsthat can be used at or above the actual bonding temperature.

In TLP and PTLP bonding, the intermediate material 52 diffuses into ametallic material and reacts with the metal coating on a compositematerial. Therefore, in an example where the fan blade 30 is fabricatedfrom a composite material and the rotor 31 is metallic, the intermediatematerial 52 may react with the metal coating 51 on the composite root 38and diffuse into the metallic rotor 31. Similarly, if the rotor 31 isfabricated from a composite material, the rotor 31 may be coated with ametal and the intermediate material 52 may react with the metal coatingon the rotor 31 as opposed to diffusion. The application of a foilintermediate material 52, a powder intermediate material 52 or a brazepaste intermediate material 52 to the root 38 is straightforward. Otherintermediate materials may be applied by PVD, electroplating or othertechniques that will be apparent to those skilled in the art.

Thus, the disclosed attachment methods can be used to join composite fanblades, airfoils or vanes to metallic or composite rotors or hubs whileaccounting for mismatches in the various CTEs of the two structures tobe joined. Further, the disclosed methods enable an optimal selection ofthe material used to fabricate the first structure (fan blade, vane)independent of the optimal selection of the material used to fabricatethe second structure (rotor, hub, etc.).

Turning to FIG. 8, a method of fabricating a fan assembly isillustrated. First, one or more fan blades 30 or vane may be formed froma composite material. The root 38 or the element that couples the fanblade 30 to a hub or rotor 31 may be coated or plated to form ametal-coated portion 51. A selected intermediate material 52 is appliedto the metal-coated portion 51 on the fan blade or vane 30. Then, thefan blade or vane 30, with its metal-coated portion 51 and intermediatematerial 52 applied to the metal-coated portion 51 is then coupled tothe rotor 31, typically by sliding the root 38, metal-coated portion 51and intermediate material 52 into a slot provided in the rotor 31 foreach fan blade or vane 30. Bonding is then carried out using TLP or PTLPbonding or brazing.

While only certain embodiments have been set forth, alternativeembodiments and various modifications will be apparent from the abovedescription to those skilled on the art. These and other alternativesare considered equivalents within the spirit and scope of thisdisclosure.

1-12. (canceled)
 13. A rotor assembly for a gas turbine engine, theassembly comprising: a composite fan blade, the fan blade including aroot; a metallic rotor including a slot for receiving the root; the rootbeing at least partially coated with a metal to form a metal-coatedportion; the metal-coated portion of the root being at least partiallycovered with an intermediate material; and the root, metal-coatedportion and intermediate material being received in the slot and bondedto the rotor.
 14. The rotor assembly of claim 13 wherein the root,metal-coated portion, intermediate material and rotor are bonded using aprocess selected from the group consisting of transient liquid phase(TLP), partial transient liquid phase (PTLP) and brazing.
 15. The rotorassembly of claim 13 wherein the composite fan blade is fabricated froma material selected from the group consisting of polyetherimide (PEI),polyimide, polyether ether ketone (PEEK), polyether ketone ketone(PEKK), polysulfone, nylon, polyphenylsulfide, polyester, condensationpolyimides, addition polyimides, epoxy cured with aliphatic and/oraromatic amines and/or anhydrides, cyanate esters, phenolics,polyesters, polybenzoxazine, polyurethanes, polyacrylates,polymethacrylates, silicones (thermoset), and any of the foregoing withfiber reinforcements.
 16. The rotor assembly of claim 13 wherein the fanblade and rotor have different coefficients of thermal expansion (CTEs)and the intermediate material has a CTE that falls between the CTEs ofthe fan blade and the rotor.
 17. The rotor assembly of claim 13 whereinthe intermediate material is a metal foil.
 18. The rotor assembly ofclaim 13 wherein the intermediate material reacts with the metal-coatedportion of the composite fan blade and diffuses into the metallic rotor.19. The rotor assembly of claim 15 wherein the composite materialfurther includes fiber reinforcements.
 20. A method of bonding a firststructure to a second structure, the method comprising: providing thefirst structure having a first CTE; providing the second structurehaving a second CTE, the first and second CTEs being different;selecting an intermediate material having a third CTE that falls betweenthe first and second CTEs; coating a portion of the first structure toprovide a metal-coated portion; applying the intermediate material tothe metal-coated portion of the first structure; and bonding the firststructure to the intermediate material and the intermediate material tothe second structure by liquid phase bonding.